GB2328442A - Conjugated polymers for luminescent devices - Google Patents

Abstract

A method for synthesising a poly(arylene vinylene), which comprises selecting a vinyl monomer by controlling the ratio of cis isomer to trans isomer in the monomer, and forming the poly(arylene vinylene) from the resulting vinyl monomer, such that the desired cis vinylene to trans vinylene ratio is obtained in the poly(arylene vinylene) product.

Description

CONJUGATED POLYMERS This invention concerns a method for the synthesis of conjugated polymers. In particular the invention concerns a method for producing photoluminescent or electroluminescent conjugated polymers for use in photoluminescent and electroluminescent devices.

Conjugated polymers and in particular poly(arylene vinylene)s (PAVs) have attracted increasing interest in recent years as potential electroluminescent and photoluminescent materials. The synthesis of such polymers has thus been the focus of much research.

A common synthetic approach in forming poly(arylene vinylenes) employs the Wessling reaction. In this reaction, a polymer is synthesised which contains arylene units, vinylene units being introduced via an elimination reaction. Such a route is capable of a small degree of selectivity, but good control over vinylene chemistry is not possible in routes which rely on elimination reactions. A route which allows the introduction of some cis vinylene into the polymer backbone is described in Science Vol. 269, page 376 (1995).

A method suitable for the synthesis of soluble poly(arylene vinylenes) is the McMurry reaction. The first effective use of this reaction in the synthesis of PAVs was reported by Feast and Millichamp in Polymer Communication, 1983, 24, 102. PAVs with a polymerisation degree of more than 100 can be produced by the reductive coupling of dialdehydes and diketones.

More recently, aryl boronic acids have been coupled with aryl halides (catalysed by palladium phosphines and sodium carbonate) to produce PAVs (Akta chemica Scandinavia 1993, 47, 221; Macromol Rapid Commun. 1996, 17, 239; Macromolecules 1996, 20, 1082; and Polymer 1989, 30, 1060) . This condensation polymerisation route is termed the Suzuki reaction and proceeds under mild conditions tolerating a varied range of functional groups. The Polymers produced show a degree of polymerisation of 100 or more.

A further route to PAVs is a coupling reaction between Grignard reagents and aryl halides, catalysed by nickel compounds. This reaction, termed the Yamamoto reaction, was applied to the preparation of unsubstituted poly-p-phenylene type polymers for the first time by Yamamoto et al in Bull Chem. Soc.

Jpn., 1978, 51, 2091. This particular reaction has been limited to the synthesis of poly-p-phenylene and has not yet been reported as a potential route to PAVs.

The inventors identified a problem in all of the above prior art methods, in that none of the methods allowed for reliable control of the cis/trans vinylene ratio in the polymer products.

Accordingly, the present invention provides a method for synthesising a poly(arylene vinylene), which method comprises selecting a vinyl monomer by controlling the ratio of cis isomer to trans isomer and forming the poly(arylene vinylene) from the vinyl monomer, such that the desired cis vinylene to trans vinylene ratio is obtained in the poly(arylene vinylene) product.

The present invention also provides a poly(arylene vinylene) obtainable according to the above method, light emitting electronic components or devices comprising the poly(arylene vinylene) and an optical component or device comprising the poly(arylene vinylene) . In the context of the present invention, a poly(arylene vinylene) is an oligomer or a polymer which contains in its backbone at least one arylene unit and at least one vinylene unit.

An advantage of the present invention is that the present synthesis allows control of the cis/trans ratio of the vinylene units in the poly(arylene vinylene) products. The invention also makes available poly(arylene vinylene)s having improved electroluminescent and photoluminescent properties, these properties being controlled by varying both the cis/trans vinylene ratio in the polymer, and the vinylene substituents of the polymers.

A further advantage is that the number of in-chain phenylene rings in the repeat units can be varied using the present method, whilst maintaining the solubility of the polymer. In addition, the larger the number of in-chain phenylene rings, the more similar in structure and properties is the polymer to those of poly(p-phenylene), which has been shown to emit in the blue region of the spectrum. By controlling the cis and trans vinylene ratio in the polymer chains it is possible to control the properties of the resultant polymers, particularly the electro-optical properties.

Any vinyl monomer can be used in the method of the present invention, provided that the ratio of the cis isomer to trans isomer in the vinyl monomer can be controlled.

Control of the ratio of cis isomer to trans isomer can be carried out by any means which in turn allows control of the ratio of cis to trans vinylene units in the polymer product.

When controlling the ratio of cis isomer to trans isomer in a monomer containing a mixture of both isomers, successive crystallisation is preferably used to select a desired isomer ratio. Alternatively, if both isomers are available in pure form, the correct cis/trans isomer ratio is preferably selected by mixing. Where the vinyl monomer is to be synthesised, the cis/trans ratio is preferably controlled by selecting the appropriate reaction conditions and/or reaction catalyst, and the appropriate purification techniques such as fractionation, distillation, recrystallisation and the various types of chromatography.

In the present invention, the poly(arylene vinylene) is preferably produced via the Yamamoto reaction or the Suzuki reaction.

The Yamamoto reaction is a coupling reaction between Grignard reagents and halides, catalysed by nickel compounds.

In the case of coupling aryl groups the reaction can be summarised according to the following reaction scheme: Ni catalyst

Ar and Ar' can be the same or different. X is a halide group, preferably a bromide group. In the context of the present invention, either or both of the Ar and Ar' groups must contain a vinyl group so that the final product is a poly(arylene vinylene) . Only one of the monomers in the above scheme need contain an aryl group to produce a PAV, but it is preferred that both monomers contain an aryl group.

The Suzuki reaction is carried out by coupling a dihalide with a boronic acid derivative. The reaction is preferably carried out in the presence of sodium carbonate and is preferably catalysed by a palladium phosphine complex. In the case of coupling aryl groups, the reaction can be represented schematically as follows:

Ar and Ar' can be the same or different. X is a halide group, preferably a bromide group. In the context of the present reaction either or both of Ar and Ar' must contain a vinyl group, so that a PAV is produced. Only one of the monomers in the above scheme need contain an aryl group to produce a PAV, but it is preferred that both monomers contain an aryl group.

When the Suzuki reaction or the Yamamoto reaction is employed in the method of the present invention, it is preferred that the vinyl monomer is a dibromide but other di halides can be used. Thus, dichloride and diiodide vinyl monomers may also be employed. If the vinyl monomer contains an aryl group then this can be polymerised in the absence of further monomers to form a poly(arylene vinylene) . However, it is preferred in the present invention that the polytarylene vinylene) is formed by copolymerising the vinyl monomer with a further monomer. If the vinyl monomer contains aryl groups then the further monomer need not be an aryl monomer. However, it is preferred in the present invention that the further monomer is an aryl monomer, such as a phenyl or biphenyl derivative.

Particularly preferred vinyl monomers for use in the present invention include 1, 2-diphenyl-l, 2-di (4-bromophenyl) -ethene, or 1,2-dimethyl-1,2-di(4-bromophenyl)-ethen In the case where the vinyl monomers themselves are to be synthesised, it is preferred that they are produced by the McMurry reaction in which a diketone or dialdehyde undergoes reductive coupling to produce a vinyl compound.

The present invention allows not only for the control of the cis/trans ratio of the vinylene units in the polymer products, but also the molecular weight of the polymers produced. It has been found that the molecular weight of the polymers is dependent upon the ratio of cis isomer to trans isomer in the vinyl starting materials as well as the solvent system which is used for polymerisation. A cis isomer to trans isomer ratio of approximately 1:1 has been found to give rise to polymers having the largest molecular weight. Similarly, solvents in which the polymers are more soluble are more likely to give rise to high molecular weight products. Accordingly, when the Suzuki reaction is employed in the present method, it is preferred that the reaction takes place in a solvent comprising THF in the presence of aqueous potassium carbonate.

The cis isomer to trans isomer ratio in the vinyl monomer is preferably from 80:20 to 20:80, more preferably 70:30 to 30:70, more preferably still 60:40 to 40:60 and most preferably 45: 55 to 55: 45.

Inevitably, polymers having a range of molecular weights are produced in any one polymerisation reaction. A poly(arylene vinylene) having the desired molecular weight can be isolated from the reaction products by fractionation.

The molecular weight of the poly(arylene vinylene) products can be affected by the duration of the reaction. In general it is preferred that the reaction is allowed to proceed for 48 hours or more, and in some cases 96 hours or more.

The PAVs produced using the method of the present invention are preferably photoluminescent and more preferably also electroluminescent. It is preferred that the photoluminescence efficiency of the PAVs is, in increasing order of preference, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more or 70% or more. It is also preferred that the electroluminescence efficiency is high, e.g. 20% or more.

Examples Yamamoto route Throughout the course of the examples, two dibromide monomers were used, namely 2,3-di (4-bromophenyl) -2-butene and 1, 2-di (4-bromophenyl) -1, 2-diphenylethene. The McMurry reaction was used to prepare these monomers from the corresponding ketones according to the following reaction scheme:

Example 1 Using the Yamamoto reaction, poly(4,4'-diphenylene dimethylvinylene)s were prepared from the corresponding dibromides, according to the following reaction scheme:

BrM)icB Br-II kelcomplexhdg THF < Throughout the synthesis of these polymers, two nickel complexes were used as catalysts, namely bis(triphenylphosphine) nickel dichloride and 1,3-bis(diphenylphosphino)propane nickel di chloride.

Seven runs were completed varying the percent of cis isomer from 100 to 80 and also varying the catalyst used and the reaction time. The results are shown in Table 1.

TABLE 1

run reaction % cis catalyst1,2 Mn Mw r DP3 time (days) isomer 1 2 100 B 1080 1800 5 2 2 90 B 1300 2110 6 3 2 80 B 1330 2480 7 4 4 80 B 1230 2110 6 5 2 100 D 2660 4000 13 6 2 90 D 2850 4600 14 7 2 80 D 2915 5000 14 iB = bis(triphenylphosphine) nickel dichloride 2D = 1,3-bis(diphenylphosphine)propane nickel dichloride 3DP = degree of polymerisation Example 2 Poly(4,4'-diphenylene diphenylvinylene)s were produced from the corresponding dibromide monomer according to the Yamamoto reaction as outlined in the following reaction scheme:

0 Br0 Br Br-(03 complex/Mg A set of three runs were carried out using a dibromide monomer having an approximately 1:1 mixture of cis and trans isomers, using three different nickel catalysts and a reaction time of two days. The results are outlined in Table 2 below.

TABLE 2

run catalyst1,2,3 Mn Mw DP4 1 B 3600 4900 11 2 C 900 1650 3 3 D 2900 3700 9 'B = bis (triphenylphosphine) nickel dichloride 2C = nickel acetylacetone 3D = 1,3-bis(diphenylphosphino)propane nickel dichloride 4DP = degree of polymerisation The polymer was recovered as a yellow precipitate and was found to give a strong greenish yellow fluorescence when irradiated with W light. Based on a results obtained in the first set of runs, polymerisations of the dibromide monomer mixture with various cis/trans isomer ratios were carried out using nickel complex B as a catalyst. The results obtained are summarised in Table 3 below.

TABLE 3

run reaction Co cis Mn Mw DP time (days) isomer 1 2 59 1200 2200 4 2 2 48 3600 4900 11 3 2 37 3300 4400 i 10 4 4 48 4300 5600 13 DP = degree of polymerisation A similar trend is observed as in the synthesis of poly(4,4'-diphenylenevinylene)s, in that the molecular weight obtained increases as the proportion of cis isomer in the monomer mixture used decreases. The number average molecular weight reaches a maximum value where an approximately 1:1 mixture of cis and trans isomers was used in the monomer. Thus in this case the use of a monomer containing approximately a 1:1 ratio of cis to trans isomer is required in order to produce a high molecular weight polymer. An increase in the reaction time from 2 to 4 days increases the degree of polymerisation.

It can be seen from the above that controlling the cis/ trans isomer ratio in the monomer when employing the Yamamoto polycondensation provides a useful route for the synthesis of poly(4,4' -diphenylene dimethylvinylene)s and poly(4,4' - diphenylene diphenylvinylene)s and related products. The cis trans ratio of vinylenes in the polymer chain can be successfully controlled using this route and this can in turn be used to control the molecular weight and luminescence properties of the polymers.

Suzuki Route The Suzuki reaction was employed using two aryl dibromides and two aryl diboronic acid monomers. The synthesis of 1,1 di (4-bromophenyl) -1, 2-diphenylethene and 2,3-di(4-bromphenyl)-2butene was carried out as described previously. In both cases the products were recovered as a mixture of cis and trans isomers which could be separated by repeated crystallisation. The isomers alone or their mixtures could be used in conjunction with either 1,4-benzene diboronic acid or 4,4'-diphenyl diboronic acid to produce structurally defined poly(arylene vinylene)s. Aryl diboronic acids were purchased from Lancaster Synthesis Ltd ( > 98k purity) and used without purification.

Example 3 Poly(tri-p-phenylene diphenylvinylene) was produced from 1,4-benzene diboronic acid and 1,2-di(4 -bromophenyl)-1,2- diphenylethene, using various ratios of cis and trans isomers in the monomer, according to the following reaction scheme:

After refluxing the reaction mixture for approximately two days, it was allowed to cool to room temperature and was concentrated by evaporating the solvent to about half of the original volume. This solution was poured into methanol and the resultant precipitate was recovered as a greenish yellow powder.

Table 4 represents the results obtained.

TABLE 4

run k cis reaction Mnl tX Dp2 mass isomer time (days) recovery3 (%) 1 62 2 1200 1800 3 6 2 48 4 1500 2000 4 53 3 48 2 1300 1700 3 46 4 37 2 1200 1600 3 8 iby GPC, "polystyrene equivalents" 2DP-Degree of polymerisation 3after re-precipitation into methanol from chloroform It was found that the recovered material was photoluminescent. It gave a palish green yellow fluorescence when exposed to W radiation. The maximum mass recovery of the product was obtained from experiments using approximately a 1:1 cis/trans ratio.

Example 4 The polymerisation procedure outlined in Example 3 was followed to prepare poly(tri-p-phenylene dimethylvinylene) from 1,4-benzene diboronic acid and 2,3-di(4-bromophenyl) -2-butene mixtures and with various cis/trans isomer ratios. The reaction scheme for the trans isomer is shown below:

The results obtained are set out in Table 5 below.

TABLE 5

run cis reaction Mnl Mi DP2 mass isomer time (days) recovery3 (%) 1 0 2 1250 1800 4 67 2 81 2 1900 2750 7 80 3 84 4 1700 2800 6 90 4 97 2 1600 2050 6 40 by GPC, "polystyrene equivalents" 2DP=degree of polymerisation 3after re-precipitation into methanol from chloroform The products were recovered as faint orange precipitates which gave a very weak orange fluorescence when irradiated with W light.

Example 5 Poly(tetra-p-phenylene diphenylvinylene was prepared via the Suzuki coupling reaction from 4,4'-biphenyl diboronic acid and 1, 2-di (4-bromophenyl) -1, 2-diphenylethene mixtures with various cis/trans isomer ratios. The polymerisation procedure established in the earlier examples was followed. The following reaction scheme illustrates the process for the trans isomer:

The results obtained are summarised in Table 6 below.

TABLE 6

run reaction % cis Mn Mwl DP1 mass time (days) isomer recovery3 (%) 1 2 0 2190 3350 5 78 2 2 32 3250 6200 7 51 3 2 48 4280 8300 9 50 4 2 62 2800 4500 6 62 5 2 100 2900 4800 6 85 6 4 32 ~ 3470 5850 7 90 as measured on pristine samples by GPC, "polystyrene equivalents" 2DP = degree of polymerisation 3after re-precipitation into methanol from chloroform The polymer was recovered as a yellow precipitate and gave a strong greenish yellow fluorescence when exposed to W light.

It can be seen that the molecular weight obtained varies with the cis/trans isomer ratio. The highest number average molecular weight was obtained when a monomer mixture with approximately a 1:1 ratio of cis to trans isomers was used in the polymerisation (see run 3).

In order to produce polymers of higher molecular weight which were free from oligomers, an equilibrium fractionation was carried cut using the samples of Table 6. As a result, polymer fractions of higher molecular weight and relatively narrow molecular weight distribution were obtained. The fractions with the highest molecular weight from each run are set out in table 7 below.

TABLE 7

run reaction % cis Mn1 Mw1 PDI DP time isomer (Mw/Mn) (days) 1 2 0 2750 4400 1.6 6 2 2 32 8300 13800 1.7 17 3 2 48 9550 15100 1.6 20 4 2 62 5000 9400 1.9 10 5 2 100 4350 7050 1.6 9 6 4 32 16300 27900 1.7 34 as measured on the highest molecular weight fraction by GPC, "polystyrene equivalents" 2DP=degree of polymerisation The same trend as observed in the polymer products is again found in the fractionated samples. The sample obtained from run 3 in which the dibromide monomer mixture with a cis/trans isomer ratio of approximately 1:1 was used gave the highest number average molecular weight. When the reaction time was extended to 4 days, a degree of polymerisation of 34 was found which corresponds to a reaction conversion of 97% of the polymer in this fraction, underlining the potential of this route to useful poly (arylene vinylene)s.

Example 6 The procedure outlined in Example 5 was followed to prepare poly (tetra-p-phenylene dimethylvinylene) from 4,4'-biphenyl diboronic acid and 2,3-di(4-bromophenyl)-2-butene mixtures with various cis/trans isomer ratios. The scheme below summarises this process for poly(tetra-p-phenylene dimethylvinylene) preparation from the trans dibromide monomer:

Products were recovered as faint yellow powders and were found to give pale yellow fluorescence under radiation. It was found that the products recovered were largely insoluble in organic solvents, thus full characterisation was not possible.

The reaction conditions used and the results obtained are summarised in Table 8 below.

TABLE 8

run % cis reaction time M,1 Mw1 mass isomer some (days) recovery2 (%) 1 0 2 * * 83 2 81 2 1126 1944 77 3 97 2 1140 1179 53 4 81 4 * * 83 as analysed on soluble portion of samples by GPC, "polystyrene equivalents" 2after re-precipitation into methanol from chloroform * samples are insoluble It can be seen from the above examples that it is possible to synthesise a poly(arylene vinylene) having a controlled cis/trans vinylene ratio in the polymer chain. The highest molecular weights are obtained using a 1:1 cis/trans vinylene ratio. This is possibly a consequence of the inherent solubility of the products. Thus fully trans polymers are likely to be rigid rods which will tend to be rather insoluble, whilst fully cis polymers will inevitably be very tightly coiled preventing solvation and also being highly insoluble. Such polymers would precipitate at an early stage in their growth and would thus have lower molecular weight. On this basis, the control of the cis/trans ratio can be used to control the molecular weight.

UV Visible absorption studies A summary of the UV absorption data for polymers prepared according to the present invention and polymers prepared according to the McMurry reaction is set out in Table 9. TABLE 9

samples synthetic % cis Mn2,3 #max (nm)4 routes isomer1 PDPV McMurry 2000 j 350 PDPV Yamamoto 48 1900 352 P3PV-DP Suzuki 48 1530 347 P4PV-DP Suzuki 48 2050 344 PDMeV Yamamoto 80 1300 290 P3PV-DMe Suzuki 80 1890 309 P4PV-DMe Suzuki 80 314 m-PPV-DP McMurry 2000 310 m-PPV-DM McMurry 1000 377 PDPV-DF McMurry 3000 400 only polymers prepared via Yamamoto and Suzuki routes could be structurally defined 2"polystyrene equivalent" values 3molecular weight of P4PV-DMe could not be determined by GPC due to poor solubility 4#max = peak of first absorption In the table, PDPV is poly(4,4'-diphenylene diphenylvinylene), P3PV-DP is poly(tri-p-phenylene diphenylefle), P4PV-DP is poly(tetra-p-phenylene dimethylvinylene), PDMeV is poly(4,4'-diphenylene dimethylvinylene), P3PV-DMe is poly(tri-pphenylene dimethylvinylene), P4PV-DMe is poly(tetra-p-phenylene dimethylvinylene), m-PPV-DP is poly(l,3-diphenylene diphenylvinylene), m-PPV-DM is poly(l,3-phenylene dimesitylvinylene) and PDPV-DF is poly(4, 4' -diphenylene-1, 2- bis(pentafluorophenyl)vinylene).

From the table it can be seen that among the polymers produced PDPV has the smallest band gap. Increasing the number of phenyl rings in the polymer repeat units was shown to increase the band gap of the resultant polymer (see PDPV, P3PV-DP and P4PV-DP).

An increase in the size of the band gap was observed when an in-chain phenyl link with a metal linkage was introduced into the polymer repeat unit (see PDPV and m-PPV-DP). However, the result from the fluorinated PDPV was unexpected in that the polymer was expected to have a larger band gap than that of the nonfluorinated analogue (see PDPV and PDPV-DF) but did not.

Replacing phenyl. with methyl as a pendant group also resulted in an increase in band gap (see for example PDPV and PDMeV).

Luminescence Studies Poly(4,4'-diphenylene diphenylvinylene) samples with varying molecular weights and cis/trans vinylene ratios were prepared via the Yamamoto polycondensation and examined for their photoluminescence characteristics. Measurements were carried out by photoexciting the samples with an Argon-ion laser which lases in the W to green region of the spectrum with two dominating lines at 351 and 364nm. The results are summarised in Table 10 below.

TABLE 10

samples W cis isomer Mnl photoluminescence efficiency(%) A ax (nm) 1 59 1200 35.0 522 2 48 1900 41.4 515 3 37 2900 35.2 523 "polystyrene equivalent" values It can be seen that photoluminescence efficiency varies with the cm trans isomer ratio of the monomer mixture used in the polymerisation. For samples of similar molecular weight the maximum efficiency was obtained from the polymer prepared using a monomer mixture with an approximately 1:1 cis/trans isomer ratio.

Poly(tetra-p-phenylene diphenyvinylene) samples were prepared with varying cis/trans vinylene contents and molecular weights, via the Suzuki coupling reaction. Photoluminescence characteristics were measured and the results are depicted in Table 11 below.

TABLE 11

samples W cis isomer M,1 photoluminescence efficiency (t) ajax (nm) 1 97 2900 28.6 524 2 62 5000 30.1 533 3 48 4200 53.5 520 4 32 2800 35.8 517 5 32 8300 32.5 521 6 32 16300 21.7 523 7 2 1800 30.7 496 "polystyrene equivalent" values It can be seen from these results that luminescence efficiency and cis/trans isomer ratio are correlated. The highest efficiency is obtained when an approximately 1:1 cis/trans isomer ratio is used. In Table 11 Samples 4-6 which contain the same cis/trans vinylene ratio, show a progressive increase in the emission peak wavelength with increase in molecular weight. This is consistent with the hypothesis that increasing molecular weight extends the conjugation length and hence decreases the band gap of the polymer. A similar trend to that found in the case of poly(4,4'-diphenylene diphenylvinylene) prepared via the Yamamoto polycondensation was observed. In particular the polymer chain which probably leads to the formation of a highly ordered conjugated polymer. In such an ordered polymer the mobility of electrons and excited species will be enhanced and this results in a higher possibility of excited species meeting photoluminescence quenching sites before decaying radiatively.

Table 11 shows that photoluminescence efficiency decreases with increasing molecular weight (see Samples 4-6) . This suggests that photoluminescence quenching sites are present in the higher molecular weight polymers which might arise from structural defects or impurities.

The above examples show that the size of the band gap in poly(arylene vinylene)s can be controlled chemically by varying the pendant groups and the number of phenyl rings in the polymer repeat unit. The photoluminescence efficiency varies with the cis/trans vinylene ratio in the polymer and maximum photoluminescence efficiency can be obtained with an approximate 1:1 ratio of cis and trans vinylene content.

Using the methods of the present invention improved photoluminescent and electroluminescent poly(arylene vinylene)s can be produced. Such polyarylene vinylenes can be used in electronic components or devices or in optical components or devices. Electronic and optical devices include photoluminescent devices, electroluminescent devices, waveguide devices and photovoltaic devices. Devices in which the polymers made according to the present invention can be used are described in WO 90/13148 and US 5,512,654.

Claims (24)

Claims:

1. A method for synthesising a poly(arylene vinylene) which method comprises selecting a vinyl monomer by controlling the ratio of cis isomer to trans isomer in the monomer, and forming the poly(arylene vinylene) from the resulting vinyl monomer, such that the desired cis vinylene to trans vinylene ratio is obtained in the poly(arylene vinylene) product.

2. A method according to claim 1, wherein the ratio of cis isomer to trans isomer is controlled using crystallization.

3. A method according to claim 1 or claim 2, wherein the vinyl monomer comprises an aryl group.

4. A method according to any preceding claim, wherein the vinyl monomer is a dihalide.

5. A method according to claim 4, wherein the vinyl monomer is a dibromide.

6. A method according to claim 5, wherein the vinyl monomer is 172-diphenyl-1,2-di(4-bromophenyl)ethene, or 1,2-dimethyl-l,2- di(4-bromophenyl)ethene.

7. A method according to any preceding claim, wherein the poly(arylene vinylene) is formed by polymerising the vinyl monomer with a further monomer.

8. A method according to claim 7, wherein the further monomer is an aryl monomer.

9. A method according to claim 8, wherein the further monomer is a phenyl derivative or a biphenyl derivative.

10. A method according to any preceding claim, wherein the poly(arylene vinylene) is formed using the Yamamoto reaction or the Suzuki reaction.

11. A method according to claim 10, wherein the Suzuki reaction is used and the reaction takes place in a solvent comprising THF in the presence of aqueous potassium carbonate.

12. A method according to any preceding claim, wherein the ratio of cis isomer to trans isomer in the vinyl monomer is controlled to from 80:20 to 20:80.

13. A method according to claim 12, wherein the ratio of cis isomer to trans isomer in the vinyl monomer is controlled to from 45:55 to 55:45.

14. A method according to any preceding claim, wherein the vinyl monomer is formed via the McMurry reaction.

15. A method according to any preceding claim, further comprising isolating the poly(arylene vinylene) by fractionation.

16. A method according to any preceding claim, wherein the reaction forming the poly(arylene vinylene) is allowed to proceed for 48 hrs or more.

17. A method according to claim 16, wherein the reaction forming the poly(arylene vinylene) is allowed to proceed for 96 hrs or more.

18. A poly(arylene vinylene) obtainable according to a method as defined in any preceding claim.

19. A poly(arylene vinylene) according to claim 18, which is photoluminescent and/or electroluminescent.

20. A poly(arylene vinylene) according to claim 19, in which the photoluminescence efficiency is 20% or more.

21. A poly(arylene vinylene) according to claim 20, in which the photoluminescence efficiency is 50% or more.

22. A light emitting electronic component or device comprising a poly(arylene vinylene) as defined in any of claims 18-21.

23. An optical component or device comprising a poly(arylene vinylene) as defined in any of claims 18-21.

24. Use of a poly(arylene vinylene) as defined in any of claims 18-21 in an electronic component or device, or in an optical component or device.